1. Field of the Invention
The present invention relates to an apparatus for elevating a squeeze roller of a liquid developing apparatus.
2. Description of the Related Art
In a general liquid electrophotographic printer, a liquid-type developing apparatus provides developer to develop an electrostatic latent image formed on a photosensitive medium such as a photoreceptor web. The liquid developing apparatus, as shown in FIG. 1, includes a developing roller 11 for providing developer injected from a nozzle 14 to an electrostatic latent image formed on a transfer surface 10a of the photoreceptor web 10 and a squeeze roller 12 for removing excess developer from the transfer surface 10a.
The squeeze roller 12 removes excess developer by pressing the photoreceptor web 10 against a backup roller 13 during a print process. Thus, during the print process, the squeeze roller 12 is required to firmly press the photoreceptor web 10 toward the backup roller 13. Also, a drip-line D that the developer leaves behind and hardens in a contact area between the squeeze roller 12 and the photoreceptor web 10 is formed due to repeated prints. To remove the drip-line D, the squeeze roller 12 must be driven in a direction reverse to that in a print mode. In a drip-line removing mode, to reduce the rotational load caused by the reverse driving of the squeeze roller 12, the pressing force of the squeeze roller 12 with respect to the photoreceptor web 10 is made lower than in the print mode. Also, when the print process is completed, the squeeze roller 12 is fully separated from the photoreceptor web 10. Thus, the liquid printer must be provided with a squeeze roller elevating apparatus which can elevate the squeeze roller 12 to press the photoreceptor web 10 and simultaneously adjust the pressing force.
FIG. 2 shows an example of a conventional squeeze roller elevating apparatus. Referring to the drawing, a sub-block 22, on which the squeeze roller 12 is installed, is installed in a main block 20 to be capable of ascending and descending. Compression springs 24 are installed between the main block 20 and the sub-block 22 to elastically bias the squeeze roller 12 toward the photoreceptor web 10. A slider 23 is installed at the main block 20 to be capable of sliding. A slanted cam groove 23a is formed in the slider 23, and a protrusion 22a formed on the sub-block 22 is inserted into the cam groove 23a and guided accordingly. Thus, when the slider 23 moves horizontally, the sub-block 22 can elevate. The slider 23 can move right and left by a cam 25 rotated by a driving source (not shown) and is elastically biased to the right as shown in the drawing by a tension spring 26.
In the squeeze roller elevating apparatus having the above structure, in all three modes, the print mode, the drip-line removing mode, and a print ready mode, the forces of the compression springs 24 and the tension spring 26 are continuously exerted. Hence, after prolonged use, the elastic forces of the compression springs 24 and the tension spring 26 are reduced so that an appropriate elastic force cannot be applied according to each mode.